The design of modified immunoglobulin molecules makes it possible to overcome the limitations of naturally-occurring antibodies. Chimeric antibodies having an antigen-binding region derived from a murine source and constant regions of human origin are described, for example, in Neuberger et al., 1985, Nature 314:268-270; and Bouhanne et al., 1984, Nature 312:643. Antibodies having constant regions modified to contain domains of different IgG isotypes are described in WO 89/07142.
There remains a need for immunoglobulin molecules offering desired features characteristic of one Ig class in combination with desired features characteristic of another Ig class. In addition, information about which domains of Ig molecules confer the desired features is needed to guide in the design of modified Ig molecules.